Discontinuous reception operation for licensed-assisted access

ABSTRACT

The present disclosure relates to a method for operating a Discontinuous Reception, DRX, function at a user equipment. The UE is configured with at least one licensed cell and at least one unlicensed cell and operates the DRX function. The UE receives, from a radio base station, a DRX-active instruction to be in DRX Active Time at least on the unlicensed cell until receiving the next downlink control information related to a downlink data transmission to be received via the unlicensed cell. Correspondingly, in response to the received DRX-active instruction, the UE is in DRX Active Time at least on the unlicensed cell, comprising continuously monitoring a downlink control channel for downlink control information.

BACKGROUND Technical Field

The present disclosure relates to methods for operating a DiscontinuousReception, DRX, function at a user equipment, wherein the user equipmentis configured with at least one licensed cell and at least oneunlicensed cell. The present disclosure also provides the user equipmentand base station for performing the methods described herein.

Description of the Related Art

Long Term Evolution (LTE)

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving a radioaccess technology that is highly competitive.

In order to be prepared for further increasing user demands and to becompetitive against new radio access technologies, 3GPP introduced a newmobile communication system which is called Long Term Evolution (LTE).LTE is designed to meet the carrier needs for high speed data and mediatransport as well as high capacity voice support for the next decade.The ability to provide high bit rates is a key measure for LTE.

The work item (WI) specification on Long-Term Evolution (LTE) calledEvolved UMTS Terrestrial Radio Access (UTRA) and UMTS Terrestrial RadioAccess Network (UTRAN) is finalized as Release 8 (LTE Rel. 8). The LTEsystem represents efficient packet-based radio access and radio accessnetworks that provide full IP-based functionalities with low latency andlow cost. In LTE, scalable multiple transmission bandwidths arespecified such as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order toachieve flexible system deployment using a given spectrum. In thedownlink, Orthogonal Frequency Division Multiplexing (OFDM)-based radioaccess was adopted because of its inherent immunity to multipathinterference (MPI) due to a low symbol rate, the use of a cyclic prefix(CP) and its affinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA)-based radioaccess was adopted in the uplink, since provisioning of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmit power of the user equipment (UE).Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniquesand a highly efficient control signaling structure is achieved in LTERel. 8/9.

LTE Architecture

The overall LTE architecture is shown in FIG. 1. The E-UTRAN consists ofan eNodeB, providing the E-UTRA user plane (PDCP/RLC/MAC/PHY) andcontrol plane (RRC) protocol terminations towards the user equipment(UE). The eNodeB (eNB) hosts the Physical (PHY), Medium Access Control(MAC), Radio Link Control (RLC) and Packet Data Control Protocol (PDCP)layers that include the functionality of user-plane header compressionand encryption. It also offers Radio Resource Control (RRC)functionality corresponding to the control plane. It performs manyfunctions including radio resource management, admission control,scheduling, enforcement of negotiated uplink Quality of Service (QoS),cell information broadcast, ciphering/deciphering of user and controlplane data, and compression/decompression of downlink/uplink user planepacket headers. The eNodeBs are interconnected with each other by meansof the X2 interface.

The eNodeBs are also connected by means of the S1 interface to the EPC(Evolved Packet Core), more specifically to the MME (Mobility ManagementEntity) by means of the S1-MME and to the Serving Gateway (SGW) by meansof the S1-U. The S1 interface supports a many-to-many relation betweenMMEs/Serving Gateways and eNodeBs. The SGW routes and forwards user datapackets, while also acting as the mobility anchor for the user planeduring inter-eNodeB handovers and as the anchor for mobility between LTEand other 3GPP technologies (terminating S4 interface and relaying thetraffic between 2G/3G systems and PDN GW). For idle-state userequipments, the SGW terminates the downlink data path and triggerspaging when downlink data arrives for the user equipment. It manages andstores user equipment contexts, e.g., parameters of the IP bearerservice, or network internal routing information. It also performsreplication of the user traffic in case of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle-mode user equipment tracking and paging procedureincluding retransmissions. It is involved in the beareractivation/deactivation process and is also responsible for choosing theSGW for a user equipment at the initial attach and at the time ofintra-LTE handover involving Core Network (CN) node relocation. It isresponsible for authenticating the user (by interacting with the HSS).The Non-Access Stratum (NAS) signaling terminates at the MME, and it isalso responsible for the generation and allocation of temporaryidentities to user equipments. It checks the authorization of the userequipment to camp on the service provider's Public Land Mobile Network(PLMN) and enforces user equipment roaming restrictions. The MME is thetermination point in the network for ciphering/integrity protection forNAS signaling and handles the security key management. Lawfulinterception of signaling is also supported by the MME. The MME alsoprovides the control plane function for mobility between LTE and 2G/3Gaccess networks with the S3 interface terminating at the MME from theSGSN. The MME also terminates the S6a interface towards the home HSS forroaming user equipments.

Component Carrier Structure in LTE

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots as shown in FIG. 2, wherein the firstdownlink slot comprises the control channel region (PDCCH region) withinthe first OFDM symbols. Each subframe consists of a given number of OFDMsymbols in the time domain (12 or 14 OFDM symbols in 3GPP LTE (Release8)), wherein each OFDM symbol spans over the entire bandwidth of thecomponent carrier. The OFDM symbols thus each consist of a number ofmodulation symbols transmitted on respective subcarriers. In LTE, thetransmitted signal in each slot is described by a resource grid ofN^(DL) _(RB)N^(RB) _(SC) subcarriers and N^(DL) _(symb) OFDM symbols.N^(DL) _(RB) is the number of resource blocks within the bandwidth. Thequantity N^(DL) _(RB) depends on the downlink transmission bandwidthconfigured in the cell and shall fulfill N^(min,DL) _(RB)<=N^(DL)_(RB)<=N^(max,DL) _(RB), where N^(min,DL) _(RB)=6 and N^(max,DL)_(RB)=110 are respectively the smallest and the largest downlinkbandwidths, supported by the current version of the specification.N^(RB) _(SC) is the number of subcarriers within one resource block. Fornormal cyclic prefix subframe structure, N^(RB) _(SC)=12 and N^(DL)_(symb) ⁼⁷.

Assuming a multi-carrier communication system, e.g., employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g., 7 OFDM symbols) and consecutive subcarriers inthe frequency domain as exemplified in FIG. 2 (e.g., 12 subcarriers fora component carrier). In 3GPP LTE (Release 8), a physical resource blockthus consists of resource elements, corresponding to one slot in thetime domain and 180 kHz in the frequency domain (for further details onthe downlink resource grid, see for example 3GPP TS 36.211, “EvolvedUniversal Terrestrial Radio Access (E-UTRA); Physical Channels andModulation (Release 8)” version 12.5.0, section 6.2, available athttp://www.3gpp.org and incorporated herein by reference).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources.

Similar assumptions for the component carrier structure will apply tolater releases too.

Carrier Aggregation in LTE-A for Support of Wider Bandwidth

The frequency spectrum for IMT-Advanced was decided at the World Radiocommunication Conference 2007 (WRC-07). Although the overall frequencyspectrum for IMT-Advanced was decided, the actual available frequencybandwidth is different according to each region or country. Followingthe decision on the available frequency spectrum outline, however,standardization of a radio interface started in the 3rd GenerationPartnership Project (3GPP). At the 3GPP TSG RAN #39 meeting, the StudyItem description on “Further Advancements for E-UTRA (LTE-Advanced)” wasapproved. The study item covers technology components to be consideredfor the evolution of E-UTRA, e.g., to fulfill the requirements onIMT-Advanced.

The bandwidth that the LTE-Advanced system is able to support is 100MHz, while an LTE system can only support 20 MHz. Nowadays, the lack ofradio spectrum has become a bottleneck of the development of wirelessnetworks, and as a result it is difficult to find a spectrum band whichis wide enough for the LTE-Advanced system. Consequently, it is urgentto find a way to gain a wider radio spectrum band, wherein a possibleanswer is the carrier aggregation functionality.

In carrier aggregation, two or more component carriers are aggregated inorder to support wider transmission bandwidths up to 100 MHz. Severalcells in the LTE system are aggregated into one wider channel in theLTE-Advanced system which is wide enough for 100 MHz even though thesecells in LTE may be in different frequency bands.

All component carriers can be configured to be LTE Rel. 8/9 compatible,at least when the bandwidth of a component carrier does not exceed thesupported bandwidth of an LTE Rel. 8/9 cell. Not all component carriersaggregated by a user equipment may necessarily be Rel. 8/9 compatible.Existing mechanisms (e.g., barring) may be used to avoid Rel-8/9 userequipments to camp on a component carrier.

A user equipment may simultaneously receive or transmit on one ormultiple component carriers (corresponding to multiple serving cells)depending on its capabilities. An LTE-A Rel. 10 user equipment withreception and/or transmission capabilities for carrier aggregation cansimultaneously receive and/or transmit on multiple serving cells,whereas an LTE Rel. 8/9 user equipment can receive and transmit on asingle serving cell only, provided that the structure of the componentcarrier follows the Rel. 8/9 specifications.

Carrier aggregation is supported for both contiguous and non-contiguouscomponent carriers with each component carrier limited to a maximum of110 Resource Blocks in the frequency domain (using the 3GPP LTE (Release8/9) numerology).

It is possible to configure a 3GPP LTE-A (Release 10)-compatible userequipment to aggregate a different number of component carriersoriginating from the same eNodeB (base station) and of possiblydifferent bandwidths in the uplink and the downlink. The number ofdownlink component carriers that can be configured depends on thedownlink aggregation capability of the UE. Conversely, the number ofuplink component carriers that can be configured depends on the uplinkaggregation capability of the UE. It may currently not be possible toconfigure a mobile terminal with more uplink component carriers thandownlink component carriers. In a typical TDD deployment, the number ofcomponent carriers and the bandwidth of each component carrier in uplinkand downlink are the same. Component carriers originating from the sameeNodeB need not provide the same coverage.

The spacing between center frequencies of contiguously aggregatedcomponent carriers shall be a multiple of 300 kHz. This is in order tobe compatible with the 100 kHz frequency raster of 3GPP LTE (Release8/9) and at the same time to preserve orthogonality of the subcarrierswith 15 kHz spacing. Depending on the aggregation scenario, the n*300kHz spacing can be facilitated by insertion of a low number of unusedsubcarriers between contiguous component carriers.

The nature of the aggregation of multiple carriers is only exposed up tothe MAC layer. For both uplink and downlink, there is one HARQ entityrequired in MAC for each aggregated component carrier. There is (in theabsence of SU-MIMO for uplink) at most one transport block per componentcarrier. A transport block and its potential HARQ retransmissions needto be mapped on the same component carrier.

When carrier aggregation is configured, the mobile terminal only has oneRRC connection with the network. At RRC connectionestablishment/re-establishment, one cell provides the security input(one ECGI, one PCI and one ARFCN) and the non-access stratum mobilityinformation (e.g., TAI) similarly as in LTE Rel. 8/9. After RRCconnection establishment/re-establishment, the component carriercorresponding to that cell is referred to as the downlink Primary Cell(PCell). There is always one and only one downlink PCell (DL PCell) andone uplink PCell (UL PCell) configured per user equipment in connectedstate. Within the configured set of component carriers, other cells arereferred to as Secondary Cells (SCells); with carriers of the SCellbeing the Downlink Secondary Component Carrier (DL SCC) and UplinkSecondary Component Carrier (UL SCC). Maximum five serving cells,including the PCell, can be configured for one UE.

The characteristics of the downlink and uplink PCell are:

-   -   For each SCell, the usage of uplink resources by the UE in        addition to the downlink ones is configurable (the number of DL        SCCs configured is therefore always larger or equal to the        number of UL SCCs, and no SCell can be configured for usage of        uplink resources only)    -   The downlink PCell cannot be de-activated, unlike SCells    -   Re-establishment is triggered when the downlink PCell        experiences Rayleigh fading (RLF), not when downlink SCells        experience RLF    -   Non-access stratum information is taken from the downlink PCell    -   PCell can only be changed with handover procedure (i.e., with        security key change and RACH procedure)    -   PCell is used for transmission of PUCCH    -   The uplink PCell is used for transmission of Layer 1 uplink        control information    -   From a UE viewpoint, each uplink resource only belongs to one        serving cell

The configuration and reconfiguration, as well as addition and removal,of component carriers can be performed by RRC. Activation anddeactivation is done via MAC control elements. At intra-LTE handover,RRC can also add, remove, or reconfigure SCells for usage in the targetcell. When adding a new SCell, dedicated RRC signaling is used forsending the system information of the SCell, the information beingnecessary for transmission/reception (similarly as in Rel-8/9 forhandover). Each SCell is configured with a serving cell index, when theSCell is added to one UE; PCell has always the serving cell index 0.

When a user equipment is configured with carrier aggregation, there isat least one pair of uplink and downlink component carriers that isalways active. The downlink component carrier of that pair might be alsoreferred to as ‘DL anchor carrier’. Same applies also for the uplink.

When carrier aggregation is configured, a user equipment may bescheduled on multiple component carriers simultaneously, but at most onerandom access procedure shall be ongoing at any time. Cross-carrierscheduling allows the PDCCH of a component carrier to schedule resourceson another component carrier. For this purpose a component carrieridentification field is introduced in the respective DCI (DownlinkControl Information) formats, called CIF.

A linking, established by RRC signaling, between uplink and downlinkcomponent carriers allows identifying the uplink component carrier forwhich the grant applies when there is no cross-carrier scheduling. Thelinkage of downlink component carriers to uplink component carrier doesnot necessarily need to be one to one. In other words, more than onedownlink component carrier can link to the same uplink componentcarrier. At the same time, a downlink component carrier can only link toone uplink component carrier.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format and other transmission-related information (e.g., HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bedynamic for each user. Generally, the L1/2 control signaling needs onlyto be transmitted once per TTI. Without loss of generality, thefollowing assumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH).

A PDCCH carries a message as a Downlink Control Information (DCI), whichin most cases includes resource assignments and other controlinformation for a mobile terminal or groups of UEs. In general, severalPDCCHs can be transmitted in one subframe.

It should be noted that in 3GPP LTE, assignments for uplink datatransmissions, also referred to as uplink scheduling grants or uplinkresource assignments, are also transmitted on the PDCCH.

Furthermore, Release 11 introduced an EPDCCH that fulfills basically thesame function as the PDCCH, i.e., conveys L1/L2 control signaling, eventhough the detailed transmission methods are different from the PDCCH.Further details can be found particularly in the current versions of3GPP TS 36.211 and 36.213, incorporated herein by reference.Consequently, most items outlined in the background and the embodimentsapply to PDCCH as well as EPDCCH, or other means of conveying L1/L2control signals, unless specifically noted.

Generally, the information sent in the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

-   -   User identity, indicating the user that is allocated. This is        typically included in the checksum by masking the CRC with the        user identity;    -   Resource allocation information, indicating the resources (e.g.,        Resource Blocks, RBs) on which a user is allocated.        Alternatively this information is termed resource block        assignment (RBA). Note, that the number of RBs on which a user        is allocated can be dynamic;    -   Carrier indicator, which is used if a control channel        transmitted on a first carrier assigns resources that concern a        second carrier, i.e., resources on a second carrier or resources        related to a second carrier; (cross carrier scheduling);    -   Modulation and coding scheme that determines the employed        modulation scheme and coding rate;    -   HARQ information, such as a new data indicator (NDI) and/or a        redundancy version (RV) that is particularly useful in        retransmissions of data packets or parts thereof;    -   Power control commands to adjust the transmit power of the        assigned uplink data or control information transmission;    -   Reference signal information such as the applied cyclic shift        and/or orthogonal cover code index, which are to be employed for        transmission or reception of reference signals related to the        assignment;    -   Uplink or downlink assignment index that is used to identify an        order of assignments, which is particularly useful in TDD        systems;    -   Hopping information, e.g., an indication whether and how to        apply resource hopping in order to increase the frequency        diversity;    -   CSI request, which is used to trigger the transmission of        channel state information in an assigned resource; and    -   Multi-cluster information, which is a flag used to indicate and        control whether the transmission occurs in a single cluster        (contiguous set of RBs) or in multiple clusters (at least two        non-contiguous sets of contiguous RBs). Multi-cluster allocation        has been introduced by 3GPP LTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive, and not allmentioned information items need to be present in each PDCCHtransmission depending on the DCI format that is used.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields asmentioned above. The different DCI formats that are currently definedfor LTE are as follows and described in detail in 3GPP TS 36.212,“Multiplexing and channel coding”, section 5.3.3.1 (current versionv12.4.0 available at http://www.3gpp.org and incorporated herein byreference). In addition, for further information regarding the DCIformats and the particular information that is transmitted in the DCI,please refer to the mentioned technical standard or to LTE—The UMTS LongTerm Evolution—From Theory to Practice, Edited by Stefanie Sesia, IssamToufik, Matthew Baker, Chapter 9.3, incorporated herein by reference.

Format 0: DCI Format 0 is used for the transmission of resource grantsfor the PUSCH, using single-antenna port transmissions in uplinktransmission mode 1 or 2.

Format 1: DCI Format 1 is used for the transmission of resourceassignments for single codeword PDSCH transmissions (downlinktransmission modes 1, 2 and 7).

Format 1A: DCI Format 1A is used for compact signaling of resourceassignments for single codeword PDSCH transmissions, and for allocatinga dedicated preamble signature to a mobile terminal for contention-freerandom access (for all transmissions modes).

Format 1B: DCI Format 1B is used for compact signaling of resourceassignments for PDSCH transmissions using closed loop precoding withrank-1 transmission (downlink transmission mode 6). The informationtransmitted is the same as in Format 1A, but with the addition of anindicator of the precoding vector applied for the PDSCH transmission.

Format 1C: DCI Format 1C is used for very compact transmission of PDSCHassignments. When format 1C is used, the PDSCH transmission isconstrained to using QPSK modulation. This is used, for example, forsignaling paging messages and broadcast system information messages.

Format 1D: DCI Format 1D is used for compact signaling of resourceassignments for PDSCH transmission using multi-user MIMO. Theinformation transmitted is the same as in Format 1B, but instead of oneof the bits of the precoding vector indicators, there is a single bit toindicate whether a power offset is applied to the data symbols. Thisfeature is needed to show whether or not the transmission power isshared between two UEs. Future versions of LTE may extend this to thecase of power sharing between larger numbers of UEs.

Format 2: DCI Format 2 is used for the transmission of resourceassignments for PDSCH for closed-loop MIMO operation (transmission mode4).

Format 2A: DCI Format 2A is used for the transmission of resourceassignments for PDSCH for open-loop MIMO operation. The informationtransmitted is the same as for Format 2, except that if the eNodeB hastwo transmit antenna ports, there is no precoding information, and forfour antenna ports, two bits are used to indicate the transmission rank(transmission mode 3).

Format 2B: Introduced in Release 9 and is used for the transmission ofresource assignments for PDSCH for dual-layer beamforming (transmissionmode 8).

Format 2C: Introduced in Release 10 and is used for the transmission ofresource assignments for PDSCH for closed-loop single-user or multi-userMIMO operation with up to 8 layers (transmission mode 9).

Format 2D: introduced in Release 11 and used for up to 8 layertransmissions; mainly used for COMP (Cooperative Multipoint)(transmission mode 10).

Format 3 and 3A: DCI formats 3 and 3A are used for the transmission ofpower control commands for PUCCH and PUSCH with 2-bit or 1-bit poweradjustments respectively. These DCI formats contain individual powercontrol commands for a group of UEs.

Format 4: DCI format 4 is used for the scheduling of the PUSCH, usingclosed-loop spatial multiplexing transmissions in uplink transmissionmode 2.

DRX—Discontinuous Reception

DRX functionality can be configured for RRC IDLE, in which case the UEuses either the specific or default DRX value (defaultPagingCycle); thedefault is broadcasted in the System Information, and can have values of32, 64, 128 and 256 radio frames. If both specific and default valuesare available, the shorter value of the two is chosen by the UE. The UEneeds to wake up for one paging occasion per DRX cycle, the pagingoccasion being one subframe. DRX functionality can be also configuredfor an “RRC CONNECTED” UE, so that it does not always need to monitorthe downlink channels. In order to provide reasonable batteryconsumption of user equipment, 3GPP LTE (Release 8/9) as well as 3GPPLTE-A (Release 10) provides a concept of discontinuous reception (DRX).Technical Standard TS 36.321, “Evolved Universal Terrestrial RadioAccess (E-UTRA); Medium Access Control (MAC) protocol specification”version 12.5.0, chapter 5.7 explains the DRX and is incorporated byreference herein.

The following parameters are available to define the DRX UE behavior;i.e., the On-Duration periods at which the mobile node is active (i.e.,in DRX Active Time), and the periods where the mobile node is in DRX(i.e., not in DRX Active Time).

On-duration: duration in downlink subframes, i.e., more in particular insubframes with PDCCH (also referred to as PDCCH subframe), that the userequipment, after waking up from DRX, receives and monitors the PDCCH. Itshould be noted here that throughout this present disclosure the term“PDCCH” refers to the PDCCH, EPDCCH (in subframes when configured) or,for a relay node with R-PDCCH configured and not suspended, to theR-PDCCH. If the user equipment successfully decodes a PDCCH, the userequipment stays awake/active and starts the inactivity timer; [1-200subframes; 16 steps: 1-6, 10-60, 80, 100, 200]

DRX inactivity timer: duration in downlink subframes that the userequipment waits to successfully decode a PDCCH, from the last successfuldecoding of a PDCCH; when the UE fails to decode a PDCCH during thisperiod, it re-enters DRX. The user equipment shall restart theinactivity timer following a single successful decoding of a PDCCH for afirst transmission only (i.e., not for retransmissions). [1-2560subframes; 22 steps, 10 spares: 1-6, 8, 10-60, 80, 100-300, 500, 750,1280, 1920, 2560] DRX Retransmission timer: specifies the number ofconsecutive PDCCH subframes where a downlink retransmission is expectedby the UE after the first available retransmission time. [1-33subframes, 8 steps: 1, 2, 4, 6, 8, 16, 24, 33]

DRX short cycle: specifies the periodic repetition of the on-durationfollowed by a possible period of inactivity for the short DRX cycle.This parameter is optional. [2-640 subframes; 16 steps: 2, 5, 8, 10, 16,20, 32, 40, 64, 80, 128, 160, 256, 320, 512, 640]

DRX short cycle timer: specifies the number of consecutive subframes theUE follows the short DRX cycle after the DRX Inactivity Timer hasexpired. This parameter is optional. [1-16 subframes]

Long DRX Cycle Start offset: specifies the periodic repetition of theon-duration followed by a possible period of inactivity for the DRX longcycle as well as an offset in subframes when on-duration starts(determined by formula defined in TS 36.321 section 5.7); [cycle length10-2560 subframes; 16 steps: 10, 20, 30, 32, 40, 64, 80, 128, 160, 256,320, 512, 640, 1024, 1280, 2048, 2560; offset is an integer between[0-subframe length of chosen cycle]]

The total duration that the UE is awake is called “Active time” or DRXActive Time. The Active Time, e.g., includes the on-duration of the DRXcycle, the time UE is performing continuous reception while theinactivity timer has not expired and the time UE is performingcontinuous reception while waiting for a downlink retransmission afterone HARQ RTT. Similarly, for the uplink the UE is awake (i.e., in DRXActive Time) at subframes where uplink retransmission grants can bereceived, i.e., every 8 ms after an initial uplink transmission untilthe maximum number of retransmissions is reached. Based on the above,the minimum Active Time is of fixed length equal to on-duration, and themaximum is variable depending on, e.g., the PDCCH activity.

The “DRX period” is the duration of downlink subframes during which a UEcan skip reception of downlink channels for battery saving purposes. Theoperation of DRX gives the mobile terminal the opportunity to deactivatethe radio circuits repeatedly (according to the currently active DRXcycle) in order to save power. Whether the UE indeed remains in DRX(i.e., is not active) during the DRX period may be decided by the UE;for example, the UE usually performs inter-frequency measurements whichcannot be conducted during the On-Duration, and thus need to beperformed at some other time, e.g., during the DRX opportunity time.

The parameterization of the DRX cycle involves a trade-off betweenbattery saving and latency. For example, in case of a web browsingservice, it is usually a waste of resources for a UE to continuouslyreceive downlink channels while the user is reading a downloaded webpage. On the one hand, a long DRX period is beneficial for lengtheningthe UE's battery life. On the other hand, a short DRX period is betterfor faster response when data transfer is resumed—for example when auser requests another web page.

To meet these conflicting requirements, two DRX cycles—a short cycle anda long cycle—can be configured for each UE; the short DRX cycle isoptional, i.e., only the long DRX cycle could be used. The transitionbetween the short DRX cycle, the long DRX cycle and continuous receptionis controlled either by a timer or by explicit commands from the eNodeB.In some sense, the short DRX cycle can be considered as a confirmationperiod in case a late packet arrives, before the UE enters the long DRXcycle. If data arrives at the eNodeB while the UE is in the short DRXcycle, the data is scheduled for transmission at the next on-durationtime, and the UE then resumes continuous reception. On the other hand,if no data arrives at the eNodeB during the short DRX cycle, the UEenters the long DRX cycle, assuming that the packet activity is finishedfor the time being.

During the Active Time, the UE monitors PDCCH, reports SRS (SoundingReference Signal) as configured and reports CQI (Channel QualityInformation)/PMI (Precoding Matrix Indicator)/RI (Rank Indicator)/PTI(Precoder Type Indication) on PUCCH. When UE is not in Active time,type-0-triggered SRS and CQI/PMI/RI/PTI on PUCCH may not be reported. IfCQI masking is set up for the UE, the reporting of CQI/PMI/RI/PTI onPUCCH is limited to the On-Duration subframes.

Available DRX values are controlled by the network and start fromnon-DRX up to x seconds. Value x may be any value as long as the pagingDRX is used in RRC IDLE. Measurement requirements and reporting criteriacan differ according to the length of the DRX interval, i.e., long DRXintervals may have more relaxed requirements (for more details seefurther below). When DRX is configured, periodic CQI reports can only besent by the UE during “active-time”. RRC can further restrict periodicCQI reports so that they are only sent during the on-duration.

FIG. 3 discloses an example of an DRX operation. The UE checks forscheduling messages (e.g., indicated by its C-RNTI, cell radio networktemporary identity, on the PDCCH) during the “on-duration” period, whichis the same for the long DRX cycle and the short DRX cycle. When ascheduling message is received during an “on-duration period”, the UEstarts an “inactivity timer” and keeps monitoring the PDCCH in everysubframe while the Inactivity Timer is running. During this period, theUE can be regarded as being in a “continuous reception mode”. Whenever ascheduling message is received while the Inactivity Timer is running,the UE restarts the Inactivity Timer, and when it expires, the UE movesinto a short DRX cycle and starts a “short DRX cycle timer” (assuming ashort DRX cycle is configured). When the short DRX cycle timer expires,the UE moves into a long DRX cycle. The short DRX cycle may also beinitiated by means of a DRX MAC Control Element, which the eNB can sendat any time to put the UE immediately into a DRX cycle, i.e., the shortDRX cycle (if so configured) or long DRX cycle (in case the short DRXcycle is not configured).

In 3GPP Release 11 a new DRX MAC control element, called Long DRXCommand MAC CE, was introduced which allows the eNB to order the UE togo immediately into the Long DRX cycle—without cycling first through theshort DRX cycle—for the case that the short DRX cycle is configured.

In addition to this DRX behavior, a ‘HARQ Round Trip Time (RTT) timer’is defined with the aim of allowing the UE to sleep during the HARQ RTT.When decoding of a downlink transport block for one HARQ process fails,the UE can assume that the next retransmission of the transport blockwill occur after at least ‘HARQ RTT’ subframes. While the HARQ RTT timeris running, the UE does not need to monitor the PDCCH. At the expiry ofthe HARQ RTT timer, the UE resumes reception of the PDCCH as normal.

The above-mentioned DRX-related timers, like the DRX-Inactivity timer,the HARQ RTT timer, the DRX retransmission timer, and the Short DRXcycle timer, are started and stopped by events such as the reception ofa PDCCH grant or a MAC control element (DRX MAC CE). Hence, the DRXstatus (active time or non-active time) of the UE can change fromsubframe to subframe and thus is not always predictable by the mobilenode.

At present, for carrier aggregation, a common DRX operation is appliedto all configured and activated serving cells of a UE; this is alsoreferred to as UE-specific DRX. Essentially, the Active Time is the samefor all cells. Hence, the UE is monitoring PDCCH of all DL Cells in thesame subframe. DRX-related timers and parameters are configured per UE,not per cell, such that there is only one DRX cycle per user equipment.All aggregated component carriers follow this “common” DRX pattern.

LTE on Unlicensed Bands—Licensed-Assisted Access LAA

In September 2014, 3GPP initiated a new study item on LTE operation onunlicensed spectrum. The reason for extending LTE to unlicensed bands isthe ever-growing demand for wireless broadband data in conjunction withthe limited amount of licensed bands. The unlicensed spectrum thereforeis more and more considered by cellular operators as a complementarytool to augment their service offering. The advantage of LTE inunlicensed bands compared to relying on other radio access technologies(RAT) such as Wi-Fi is that complementing the LTE platform withunlicensed spectrum access enables operators and vendors to leverage theexisting or planned investments in LTE/EPC hardware in the radio andcore network.

However, it has to be taken into account that unlicensed spectrum accesscan never match the qualities of licensed spectrum access due to theinevitable coexistence with other radio access technologies (RATs) inthe unlicensed spectrum. LTE operation on unlicensed bands willtherefore at least in the beginning be considered a complement to LTE onlicensed spectrum rather than as stand-alone operation on unlicensedspectrum. Based on this assumption, 3GPP established the term LicensedAssisted Access (LAA) for the LTE operation on unlicensed bands inconjunction with at least one licensed band. Future stand-aloneoperation of LTE on unlicensed spectrum without relying on LAA howevershall not be excluded.

The currently-intended general LAA approach at 3GPP is to make use ofthe already specified Rel-12 carrier aggregation (CA) framework as muchas possible, where the CA framework configuration as explained beforecomprises a so-called primary cell (PCell) carrier and one or moresecondary cell (SCell) carriers. CA supports in general bothself-scheduling of cells (scheduling information and user data aretransmitted on the same component carrier) and cross-carrier schedulingbetween cells (scheduling information in terms of PDCCH/EPDCCH and userdata in terms of PDSCH/PUSCH are transmitted on different componentcarriers). This includes that a common DRX scheme is used for LAA,particularly if it does not result in a need for very short DRXcycles/very long Active Times. As with carrier aggregation mentionedabove, “common DRX” scheme in this respect means that the UE operatesthe same DRX for all aggregated and activated cells, includingunlicensed and licensed cells. Consequently, the Active Time is the samefor all serving cells, e.g., UE is monitoring PDCCH of all downlinkserving cells in the same subframe; the DRX-related timers andparameters are configured per UE.

A very basic scenario is illustrated in FIG. 4, with a licensed PCell,licensed SCell 1, and various unlicensed SCells 2, 3, and 4 (exemplarilydepicted as small cells). The transmission/reception network nodes ofunlicensed SCells 2, 3, and 4 could be remote radio heads managed by theeNB or could be nodes that are attached to the network but not managedby the eNB. For simplicity, the connection of these nodes to the eNB orto the network is not explicitly shown in the figure.

At present, the basic approach envisioned at 3GPP is that the PCell willbe operated on a licensed band while one or more SCells will be operatedon unlicensed bands. The benefit of this strategy is that the PCell canbe used for reliable transmission of control messages and user data withhigh quality of service (QoS) demands, such as for example voice andvideo, while an SCell on unlicensed spectrum might yield, depending onthe scenario, to some extent significant QoS reduction due to inevitablecoexistence with other RATs.

It has been agreed during RAN1#78bis that the LAA investigation at 3GPPwill focus on unlicensed bands at 5 GHz. One of the most critical issuesis therefore the coexistence with Wi-Fi (IEEE 802.11) systems operatingat these unlicensed bands. In order to support fair coexistence betweenLTE and other technologies such as Wi-Fi as well to guarantee fairnessbetween different LTE operators in the same unlicensed band, the channelaccess of LTE for unlicensed bands has to abide by certain sets ofregulatory rules which depend on a region and particular frequency band;a comprehensive description of the regulatory requirements for allregions for operation on unlicensed bands at 5 GHz is given inR1-144348, “Regulatory Requirements for Unlicensed Spectrum”,Alcatel-Lucent et al., RAN1#78bis, September 2014, incorporated hereinby reference. Depending on a region and band, regulatory requirementsthat have to be taken into account when designing LAA procedurescomprise Dynamic Frequency Selection (DFS), Transmit Power Control(TPC), Listen Before Talk (LBT) and discontinuous transmission withlimited maximum transmission duration. The intention of 3GPP is totarget a single global framework for LAA which basically means that allrequirements for different regions and bands at 5 GHz have to be takeninto account for the system design.

The listen-before-talk (LBT) procedure is defined as a mechanism bywhich an equipment applies a clear channel assessment (CCA) check beforeusing the channel. The CCA utilizes at least energy detection todetermine the presence or absence of other signals on a channel in orderto determine if a channel is occupied or clear, respectively. Europeanand Japanese regulations mandate the usage of LBT in the unlicensedbands. Apart from regulatory requirements, carrier sensing via LBT isone way for fair sharing of the unlicensed spectrum, and hence it isconsidered to be a vital feature for fair and friendly operation in theunlicensed spectrum in a single global solution framework.

In an unlicensed spectrum, channel availability cannot always beguaranteed. In addition, certain regions such as Europe and Japanprohibit continuous transmission and impose limits on the maximumduration of a transmission burst in the unlicensed spectrum. Hence,discontinuous transmission with limited maximum transmission duration isa required functionality for LAA.

DFS is required for certain regions and bands in order to detectinterference from radar systems and to avoid co-channel operation withthese systems. The intention is furthermore to achieve a near-uniformloading of the spectrum. The DFS operation and correspondingrequirements are associated with a master-slave principle. The mastershall detect radar interference, can however rely on another device,associated with the master, to implement radar detection.

The operation on unlicensed bands at 5-GHz is in most regions limited torather low transmit power levels compared to the operation on licensedbands which results in small coverage areas. Even if the licensed andunlicensed carriers were to be transmitted with identical power, usuallythe unlicensed carrier in the 5 GHz band would be expected to support asmaller coverage area than a licensed cell in the 2 GHz band due toincreased path loss and shadowing effects for the signal. A furtherrequirement for certain regions and bands is the use of TPC in order toreduce the average level of interference caused for other devicesoperating on the same unlicensed band.

Detailed information can be found in the harmonized European standardETSI EN 301 893, current version 1.8.0, incorporated herein byreference.

Following this European regulation regarding LBT, devices have toperform a Clear Channel Assessment (CCA) before occupying the radiochannel with a data transmission. It is only allowed to initiate atransmission on the unlicensed channel after detecting the channel asfree based, e.g., on energy detection. In particular, the equipment hasto observe the channel for a certain minimum time (e.g., for Europe 20μs, see ETSI 301 893, under clause 4.8.3) during the CCA. The channel isconsidered occupied if the detected energy level exceeds a configuredCCA threshold (e.g., for Europe, −73 dBm/MHz, see ETSI 301 893, underclause 4.8.3), and conversely is considered to be free if the detectedpower level is below the configured CCA threshold. If the channel isdetermined as being occupied, it shall not transmit on that channelduring the next Fixed Frame Period. If the channel is classified asfree, the equipment is allowed to transmit immediately. The maximumtransmit duration is restricted in order to facilitate fair resourcesharing with other devices operating on the same band.

The energy detection for the CCA is performed over the whole channelbandwidth (e.g., 20 MHz in unlicensed bands at 5 GHz), which means thatthe reception power levels of all subcarriers of an LTE OFDM symbolwithin that channel contribute to the evaluated energy level at thedevice that performed the CCA.

Furthermore, the total time during which an equipment has transmissionson a given carrier without re-evaluating the availability of thatcarrier (i.e., LBT/CCA) is defined as the Channel Occupancy Time (seeETSI 301 893, under clause 4.8.3.1). The Channel Occupancy Time shall bein the range of 1 ms to 10 ms, where the maximum Channel Occupancy Timecould be, e.g., 4 ms as currently defined for Europe. Furthermore, thereis a minimum Idle time the UE is not allowed to transmit after atransmission on the unlicensed cell, the minimum Idle time being atleast 5% of the Channel Occupancy Time. Towards the end of the IdlePeriod, the UE can perform a new CCA, and so on. This transmissionbehavior is schematically illustrated in FIG. 5, the figure being takenfrom ETSI EN 301 893 (there FIG. 2: “Example of timing for Frame BasedEquipment”).

Considering the different regulatory requirements, it is apparent thatthe LTE specification for operation in unlicensed bands will requireseveral changes compared to the current Rel-12 specification that islimited to licensed band operation. The currently-defined DRX operationcan have several disadvantages when being applied by UEs having anaggregated unlicensed cell.

BRIEF SUMMARY

One non-limiting and exemplary embodiment provides an improved methodfor operating a Discontinuous Reception, DRX, function at a userequipment, which is configured with at least one unlicensed cell.

In one general aspect, the techniques disclosed here feature a methodfor operating a Discontinuous Reception, DRX, function at a userequipment. The user equipment is configured with at least one licensedcell and at least one unlicensed cell and operates the DRX function. Themethod includes receiving by the user equipment, from a radio basestation, a DRX-active instruction to be in DRX Active Time at least onthe unlicensed cell until receiving the next downlink controlinformation related to a downlink data transmission to be received viathe unlicensed cell. In response to the received DRX-active instruction,the user equipment is in DRX Active Time at least on the unlicensedcell, comprising continuously monitoring a downlink control channel fordownlink control information.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary downlink resource grid of a downlink slot of asubframe as defined for 3GPP LTE (Release 8/9);

FIG. 3 illustrates the DRX operation of a mobile terminal, and inparticular the DRX opportunity and on-duration periods, according to ashort and long DRX cycle;

FIG. 4 illustrates an exemplary licensed-assisted access scenario, withvarious licensed and unlicensed cells;

FIG. 5 illustrates schematically the transmission timing on anunlicensed band, including the different periods, Channel OccupancyTime, Idle Period, and Fixed Frame Period;

FIG. 6 illustrates schematically the DRX operation for an exemplaryscenario with one unlicensed cell, and the timing of correspondingdownlink transmissions via the unlicensed cell;

FIG. 7 illustrates schematically an enhanced DRX operation and thetiming of corresponding downlink transmissions via the unlicensed cellaccording to one embodiment;

FIG. 8 illustrates schematically an enhanced DRX operation and thetiming of corresponding downlink transmissions via the unlicensed cellaccording to a further embodiment;

FIG. 9 illustrates schematically an enhanced DRX operation and thetiming of corresponding downlink transmissions via the unlicensed cellaccording to a further embodiment;

FIG. 10 is a sequence diagram for the enhanced DRX operation in a UEaccording to a further embodiment;

FIG. 11 illustrates schematically an enhanced DRX operation and thetiming of corresponding downlink transmissions via the unlicensed cellaccording to the embodiment discussed in FIG. 10; and

FIG. 12 illustrates schematically an enhanced DRX operation and thetiming of corresponding downlink transmissions via the unlicensed cellaccording to a variation of the embodiment discussed in FIGS. 10 and 11.

DETAILED DESCRIPTION

A mobile station or mobile node or user terminal or user equipment is aphysical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The term “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency resources.

The term “unlicensed cell” or alternatively “unlicensed carrier” as usedin the set of claims and in the application is to be understood broadlyas a cell/carrier in an unlicensed frequency band. Correspondingly, theterm “licensed cell” or alternatively “licensed carrier” as used in theset of claims and in the application is to be understood broadly as acell/carrier in a licensed frequency band. Exemplarily, these terms areto be understood in the context of 3GPP as of Release 12/13 and theLicensed-Assisted Access Work Item.

The expression “be in DRX Active Time” as used in the set of claims andin the application is to be understood broadly as a subframe where themobile station monitors the physical control channel like PDCCH orEPDCCH for downlink control information (DCI). Upon detection ofdownlink control information certain actions are performed by the mobileterminal, e.g., as described in the background section. Correspondinglythe term “to be not in DRX Active Time” as used in the set of claims andin the application is to be understood broadly as a subframe where themobile station is not required to monitor the physical control channellike PDCCH or EPDCCH for downlink control information (DCI).

As discussed in the background section, the LTE specification foroperation in unlicensed bands will require several changes compared tothe current Release-12 specification for licensed band operation. Theco-existence with WiFi on unlicensed bands at 5 GHz is one of the mostcritical topics. As stipulated by the European Regulation Requirements,nodes operating on unlicensed bands are to perform Listen-Before-Talkbefore accessing the channel, which is based, e.g., on the receptionpower level at the node over the whole frequency band.

As explained in the background section, 3GPP agreed so far that a commonDRX operation for all aggregated and activated cells is assumed for a UEalso in case of unlicensed cells, so as to reuse existing mechanism asapplied to the usual carrier aggregation. In particular, the same DRXoperations apply to all serving cells, including an identical DRX ActiveTime during which the PDCCHs of the various cells are monitored. Itshould be noted that throughout this present disclosure the term “PDCCH”refers to the PDCCH, EPDCCH (in subframes when configured) or, for arelay node with R-PDCCH configured and not suspended, to the R-PDCCH.

However, there are several differences between DRX for carrieraggregation as already known and DRX applied in an LAA scenario. For onething, due to having to perform LBT/CCA before transmitting on anunlicensed cell, there is no guarantee that the channel on theunlicensed cell is actually obtained for performing the transmission.Furthermore, regulatory requirements restrict the time of a continuoustransmission to a maximum Channel occupancy time, such that, even if thechannel is determined by the CCA to be free, the transmitter (in thiscase the radio base station, eNodeB) can only be occupying the channelfor a limited amount of time.

FIG. 6 illustrates the DRX operation with two serving cells (PCell andone unlicensed cell) as well as data downlink transmissions (PDSCH) andthe corresponding downlink control information (PDCCH). FIG. 6furthermore illustrates in which subframes the UE is in DRX Active Timeand in which the UE is not. In the exemplary scenario of FIG. 6, crossscheduling from the PCell is assumed, i.e., downlink control information(for downlink and uplink) relating to the unlicensed cell is receivedvia the PCell instead of the unlicensed cell itself (which could betermed self scheduling). For illustration purposes only, the DRXOn-Duration period is assumed to be 3 subframes long, the Short or LongDRX cycle to be 32 subframes long, the DRX Inactivity Timer to expirewithin 2 subframes, the maximum Channel Occupancy Time (termed “Max trxduration” in FIG. 6) to be 5 ms (subframes), and the Idle Period to be 2ms (subframes).

A further assumption to facilitate explanation of the underlyingtechnical problems to be solved by the various embodiments is that theUE is not in DRX Active Time for other reasons, e.g., HARQ RTT timerrunning or SR on PUCCH has been sent. In other words, the otheravailable conditions (e.g., HARQ RTT timer,mac-ContentionResolutionTimer, SR pending, UL grant, etc.) due to whicha UE can be in DRX Active Time are ignored, and focus is put on the DRXInactivity Timer.

The eNB can only perform a downlink transmission via an unlicensed cellin those subframes during which the UE monitors the corresponding PDCCHwhich is received via the PCell. In other words, in order for the UE tobe able to receive a downlink transmission from the eNodeB, the UE mustbe in DRX Active Time (at least on the unlicensed cell and thescheduling cell, PCell) so as to monitor the corresponding downlinkcontrol channel. For example, the UE would monitor the PDCCH on thePCell during subframes of the DRX On-Duration period, and the eNB couldcorrespondingly transmit a PDCCH, PDSCH in one of said subframes of theDRX On-Duration period (in FIG. 6, subframe 2 of the first depictedradio frame). It is assumed that the channel of the unlicensed cell isnot occupied, such that an LBT/CCA performed by the eNodeB in a timelymanner before initiating the transmission is successful. Uponsuccessfully decoding the first PDCCH, the corresponding DRX InactivityTimer would be running, and re-started upon every new successfuldecoding of a PDCCH.

The eNB could transmit data in 5 consecutive subframes (i.e., maximumchannel occupancy time); termed 1st data burst in FIG. 6. Thecorresponding DRX Inactivity Timer would be running 2 subframes longer,i.e., until subframe 8, such that the UE would still be in DRX ActiveTime until subframe 8, with subframe 9 being the first subframe wherethe UE is not in DRX Active Time. However, the idle period of 2 ms forthe unlicensed cell after the end of the 1st data burst prevents the eNBto (do the LBT/CCA and to) transmit again before subframe 9.Consequently, the eNB has to wait until the next time where the UE is inDRX Active Time, which is the first subframe of the next On-Durationperiod (in this case beginning with subframe 32). Again, assuming theLBT/CCA to be successfully performed by the eNodeB, a second data burst,including corresponding downlink control information (PDCCH) and datatransmission (PDSCH), can be performed in 5 consecutive subframes,subframes 32-36. Such a transmission mechanism is then performedrepetitively.

As can be appreciated from the above description, such a datatransmission is rather inefficient and may take a long time to becompleted not only due to the short time possible for the data bursts onunlicensed cells but also due to the few downlink opportunitiesavailable during normal DRX operation. This is further exacerbatedassuming that the frequency band of the unlicensed cell is also used bya WLAN node, in which case the LBT/CCA performed by the eNodeB would notthe successful many times.

The described problem depends also on the particular parameters chosenfor the DRX function. By choosing short DRX cycles and long DRX ActiveTime periods for a UE with (at least one) unlicensed cell, the problemis mitigated since the eNB will get more opportunities to try performinga downlink transmission (including performing LBT/CCA). However, thiscomes at the cost of expending a lot of power.

The following exemplary embodiments are conceived by the inventors tomitigate the problems explained above.

Some of these are to be implemented in the wide specification as givenby the 3GPP standards and explained partly in the background section,with the particular key features being added as explained in thefollowing pertaining to the various embodiments. It should be noted thatthe embodiments may be advantageously used for example in a mobilecommunication system, such as 3GPP LTE-A (Release 10/11/12/13)communication systems as described in the background section above, butthe embodiments are not limited to its use in this particular exemplarycommunication networks.

The explanations should not be understood as limiting the scope of thedisclosure, but as a mere example of embodiments to better understandthe present disclosure. A skilled person should be aware that thegeneral principles of the present disclosure as laid out in the claimscan be applied to different scenarios and in ways that are notexplicitly described herein. Correspondingly, the following scenariosassumed for explanatory purposes of the various embodiments shall notlimit the present disclosure and its embodiments as such.

According to one embodiment which solves the above described problem, aPDCCH is repetitively transmitted from the eNB (for example on thePCell, being the scheduling cell of the unlicensed cell) so as to keepthe UE in DRX Active Time as long as necessary to allow the eNB toinitiate the next downlink transmission on the unlicensed cell. Thisembodiment will be explained in connection with FIG. 7, whichillustrates the DRX operation and downlink transmission for two cells (aPCell, and one unlicensed serving cell, e.g., SCell) with which a UE isconfigured. A similar scenario as for FIG. 6 is assumed, additionallyillustrating the various additional PDCCHs and the correspondingadditional subframes the UE is in DRX Active Time.

In particular, so as to achieve that the UE is in DRX Active Time (i.e.,monitors for PDCCHs) when the eNB schedules the next downlinktransmission on the unlicensed cell (assuming CCA was successful), theDRX Inactivity Timer is periodically restarted (in a timely mannerbefore its expiry) by transmitting corresponding PDCCHs in the downlink(for example via the PCell). It should be noted that these additionalPDCCHs needed not refer to the unlicensed cell (although they could),but can refer (as in this exemplary case) to a downlink transmission onthe PCell itself. Since common DRX operation on all cells is assumed,the PDCCH on the PCell achieves that the DRX Active Time in both PCelland the unlicensed cell continues. The time period in which the UE is inDRX Active Time can thus be extended as long as the eNB deems itnecessary.

As illustrated in FIG. 7, after receiving the last PDCCH/PDSCH for thefirst data burst in subframe 6, the first additional PDCCH can betransmitted in subframe 8, i.e., before expiry of the DRX Inactivitytimer (2 subframes after the last PDCCH reception in subframe 6). Inthis exemplary scenario, it is assumed that the additional PDCCHschedules a PDSCH transmission on the PCell, as illustrated in FIG. 7.

The additional PDCCH prevents the DRX Inactivity timer to expire and thecorresponding subframes 9 and 10 will be part of the DRX Active Time forthe UE as well. It is assumed for the exemplary scenario of FIG. 7 thatthe eNodeB performs the LBT/CCA periodically after the end of the idleperiod, i.e., as of subframe 9, however, it is further assumed that theLBT/CCA is not successful, i.e., that the channel is occupied and notusable for the eNodeB to perform the second data burst yet.

Correspondingly, in order to keep the UE further in DRX Active Timeuntil the CCA is successful, additional PDCCHs are transmitted so as tokeep the DRX Inactivity Timer running, the next PDCCH being transmittedin subframe 10, then in subframes 12, 14, 16, 18, and 20. It is thenassumed that LBT/CCA is performed successfully in subframe 21 (e.g., aWLAN node finished a transmission), such that the second data burst canbe performed in corresponding subframes 22-26 (in 5 continuoussubframes, limited by the maximum channel occupancy time).

However, depending on the length of the Idle Time, the DRX InactivityTimer, and unlicensed channel occupation, quite a significant number ofPDCCHs needs to be sent to keep the UE in DRX Active Time. This willconsequently increase the signaling overhead (PDCCH/PDSCH) and reducethe PDCCH capacity. Furthermore, each of the additional PDCCHs wouldschedule a corresponding downlink or uplink transmission (i.e., PDSCH,PUSCH) with either dummy data (if, e.g., no uplink or downlink data isavailable for transmission) or with data actually pending fortransmission (e.g., part of the downlink data to be transmitted via theunlicensed cell), which would then be transmitted via the PCell. Even ifas few data as possible is scheduled, the PDSCH/PUSCH capacity of thePCell would still be reduced. It should be noted that (unlicensed)serving cells shall offload data from the PCell, which would not be thecase here anymore.

Another embodiment which solves the above described problem is that theUE is in DRX Active Time in all subframes in which the unlicensed cellis activated. Put differently, all subframes where the unlicensed cellis activated are part of the DRX Active Time where the UE continuouslymonitors for PDCCHs (e.g., on the PCell). This has the advantage that itdoes not require any signaling (e.g., the previously-mentionedadditional PDCCH(s) of FIG. 7) to keep the mobile in DRX Active Time, asthis is done implicitly based on the activation and deactivation statusof the unlicensed cell. When assuming a common DRX for all aggregatedand configured cells of the UE, this basically means that the UE is inDRX Active Time in all subframes of all aggregated cells where at leastone unlicensed cell is activated.

This might not be very efficient from the perspective of UE powersaving, but this disadvantage may be mitigated by correspondinglydeactivating and activating the unlicensed cell as necessary, which willbe described in the following. Cell deactivation and activation ispossible for example by use of a corresponding Activation/DeactivationMAC Control Element as defined in subclause 6.1.3.8 of 3GPP TS 36.321v12.5.0, incorporated herein by reference. Of course, the instruction todeactivate and activate a cell could be implemented differently.Correspondingly, an eNB can use this MAC CE to activate and deactivatethe unlicensed cell in a suitable manner to save power while still beingable to assure that the UE is continuously in DRX Active Time whendownlink data is to be transmitted via the unlicensed cell.

FIG. 8 illustrates in said respect that, although the DRX InactivityTimer expires, the UE is still in DRX Active Time in subframes 9, 10,11, etc. Correspondingly, in all subframes in which the unlicensed cellis activated, the UE is in DRX Active Time on allconfigured/aggregated/activated cells (here PCell, and the oneunlicensed cell; common DRX is assumed). Therefore, the eNB is able tosend the 2nd data burst as soon as LBT/CCA is performed by the eNodeBsuccessfully (exemplary be assumed to take place in subframe 21 in asimilar manner as already explained in connection with FIG. 7).

It is then assumed that no further data is to be transmitted, and, forpower saving purposes, the eNB decides to deactivate the unlicensed cellby transmitting a corresponding deactivation instruction (in FIG. 8termed exemplarily LAA cell deactivation) to the UE (e.g., via thePCell) (e.g., the above-mentioned MAC CE). In the exemplary scenario ofFIG. 8, it is assumed that this is done in subframe 27, such that theunlicensed cell is deactivated as of subframe 28 (neglecting here anysignaling and process delay typically involved in theactivation/deactivation procedure for illustration purposes); theinactive subframes of the unlicensed cell are shown with dotted-linedsubframe boxes in FIG. 8). Due to the deactivated unlicensed cell, theUE is not in DRX Active Time on the PCell in subframes 30 and 31 (DRXInactivity Timer restarted by the LAA cell deactivation expires insubframe 29). According to the normal DRX operation, the periodical DRXOn-Duration period causes the UE to be in DRX Active Time in subframes32-34 on the PCell.

In the exemplary scenario of FIG. 8, it is further assumed that the eNBdecides to activate the unlicensed cell again (e.g., because downlinkdata is to be transmitted, and the unlicensed cell shall be used in saidrespect to not cause load on the PCell). Correspondingly, the eNB usesthe last subframe 34 of the On-Duration period to transmit a suitablecell activation command to the UE (via the PCell), such that theunlicensed cell is again activated as of subframe 35 (again, it isassumed for illustration purposes that there is no activation delaycaused by signaling and processing). Consequently, the UE is in DRXActive Time as of subframe 35 on the PCell and the unlicensed cell,independently from expiry of the DRX Inactivity Timer (and other DRXActive Time conditions, such as HARQ RTT timer, SR pending, etc). Insubframes 35 and 36, the UE would have been in DRX Active Time also dueto the running DRX inactivity timer, but as of subframe 36, theDRX-active instruction ensures that the UE is in DRX Active Time too.

As soon as the unlicensed cell is determined to be not occupied (i.e.,LBT/CCA by eNB is successful), the eNB may perform a correspondingdownlink transmission on the unlicensed cell, here are assumed to takeplace in subframes 40-44 (including corresponding PDCCHs on the PCelland PDSCHs on the unlicensed cell).

When assuming a particular implementation in the 3GPP environment,particularly as described in the background section, one exemplaryimplementation of the embodiment can foresee an additional condition forthe UE to check whether a particular subframe shall be DRX Active Timeor not. In particular, currently the 3GPP technical standard 36.321,current version 12.5.0, defines in section 5.7 several conditions:

When a DRX cycle is configured, the Active Time includes the time while:

-   -   onDurationTimer or drx-InactivityTimer or        drx-RetransmissionTimer or mac-ContentionResolutionTimer (as        described in subclause 5.1.5) is running; or    -   a Scheduling Request is sent on PUCCH and is pending (as        described in subclause 5.4.4); or    -   an uplink grant for a pending HARQ retransmission can occur and        there is data in the corresponding HARQ buffer; or    -   a PDCCH indicating a new transmission addressed to the C-RNTI of        the MAC entity has not been received after successful reception        of a Random Access Response for the preamble not selected by the        MAC entity (as described in subclause 5.1.4).

According to this exemplary implementation of the solution, thefollowing additional condition could be foreseen:

-   -   When a DRX cycle is configured, the Active Time includes the        time while an unlicensed serving cell (SCell) is activated.

Of course, the formulation of the condition chosen above is merely anexample and other suitable formulations/terminology could be equallyused in said respect. Consequently, a UE operating according to DRXshall additionally check in each subframe whether an aggregatedunlicensed cell is activated, and, if so, to be in DRX Active Time insaid subframe, which entails performing actions as specific for DRXActive Time (see also TS 36.321, section 5.7 for details).

A further implementation of this embodiment considers the operation of acell deactivation timer that can be configured in a UE and which is atimer that, upon expiry, triggers a corresponding cell to bedeactivated. As defined in the current 3GPP specification TS 36.321v12.5.0, subclause 5.13, incorporated herein by reference, ansCellDeactivationTimer can be running, where the UE shall deactivate theSCell upon its expiry. While the PCell cannot be deactivated by such atimer, this may well be the case for any of the other (un)licensed cellswith which the UE is configured. As explained above, the presentsolution provides a DRX operation which is based on anactivation/deactivation status of the unlicensed cell. Furthermore, forpower saving purposes the eNodeB may explicitly activate and deactivatethe unlicensed cell via a command so as to influence the DRX operationon the remaining cells configured for the UE (assuming common DRX). Inparallel however, the cell deactivation timer may be running in the UEfor each serving cell and may thus cause the unlicensed cell to bedeactivated although it should remain activated so as to be able toreceive the next downlink transmission from the eNodeB. According tothis exemplary implementation, the function of the cell deactivationtimer can be ignored in said respect, and deactivation activation of theSCells shall be controlled by corresponding explicitactivation/deactivation commands from the eNodeB.

Still another embodiment which solves the above-described problem issimilar to the previous embodiment explained in connection with FIG. 8in that the DRX Active Time is again implicitly controlled by theactivation/deactivation status of the unlicensed cell. However, thedifference is that for the present embodiment a separate DRX operationis assumed, instead of the common DRX operation assumed so far. Inparticular, although at present common DRX operation on all aggregatedand configured carriers of a UE is agreed in 3GPP, this may change inthe future, such that a common DRX operation for all cells configuredfor a UE is no longer required. Correspondingly, depending on the actualimplementation and UE configuration, different carriers of a UE could beoperated with a different DRX function, meaning that the UE could (notnecessarily would) be in DRX Active Time in different subframes fordifferent carriers. For explaining this solution, reference is made alsoto FIG. 9 which is an exemplary schematic illustration where a UE withthree configured cells is assumed: a PCell, an unlicensed cell, and oneSCell. It should be noted that the unlicensed cell could be basicallyalso treated as an SCell. Cross-scheduling is still assumed such thatthe scheduling for the unlicensed cell is received via the PCell; thePCell can thus be termed exemplarily the “scheduling cell” of theunlicensed cell.

According to this solution, the DRX function for the PCell (as thescheduling cell of the unlicensed cell) and the unlicensed cell areoperated in common by the UE; i.e., a common DRX for the PCell andunlicensed cell is used by the UE. On the other hand, the DRX operationon the SCell (and any other licensed cell, if configured for the UE) isseparate from the common DRX of the PCell and unlicensed cell.

Correspondingly, the DRX operation for the PCell and the unlicensed cellcan be basically the same as explained for the previous solution,exemplary as illustrated in FIG. 8, as can be seen from FIG. 9.

On the other hand, the DRX operation for the SCell is notaffected/changed by the common DRX operation on the PCell and unlicensedcell, since it is separate therefrom. In the exemplary scenario of FIG.9, the DRX operation for the SCell is not only separate but is alsooperated with different parameters, in this case a DRX On-Duration of 4subframes and a Short/Long DRX cycle of 20 ms. Of course, otherparameters or exactly the same parameters as for the common DRX could bechosen as well. Further, the DRX parameters could be UE-specific (i.e.,the same for all carriers) even though no common DRX operation would beperformed. In the exemplary scenario of FIG. 9, the DRX operationfollows the DRX cycle for the SCell such that the UE is on the SCell inDRX Active Time at least according to the DRX On-Duration periods insubframes 0-3, 20-23, and 40-43.

In the exemplary scenario of FIG. 9, cross scheduling of the unlicensedcell from the PCell was assumed. In case the UE receives the PDCCHdestined for the unlicensed cell via the unlicensed cell itself (i.e., aself-scheduling scenario) and not via the PCell, the DRX operation onthe unlicensed cell would be separate from the DRX operation of theremaining cells (i.e., the PCell and the SCell, and optionally also fromother unlicensed cells if configured for the UE), the remaining cells inturn could or could not be operated in common. According to oneadditional embodiment of the present disclosure, there would be two DRXoperations running in the UE, i.e., one for the common DRX operation forall unlicensed cells and one common DRX operation across all aggregatedlicensed cells. Correspondingly, the UE would be in DRX Active Time onthe unlicensed cell in all subframes where at least one unlicensed cellis activated (in the same manner as for the cross-scheduling casediscussed before). As before, the eNB can deactivate/activate anunlicensed cell as necessary to save power and thus to avoid that the UEis always in DRX Active Time.

On the other hand, since the DRX operations on the PCell and the SCellare separate from the one on the unlicensed cell(s), the UE would followthe normal DRX pattern(s) as configured for the PCell and the SCellindependently from the activation/deactivation status of the unlicensedcell.

A further solution to the above described problem according to thefollowing exemplary embodiment(s) will be presented in detail in thefollowing. These exemplary embodiments will be described so as tohighlight the underlying principles and shall thus not be understood aslimiting the present disclosure. As before, to facilitate illustration,various assumptions are made, which however should be regarded as notrestricting the present disclosure. As before, it is assumed that a UEis already set up and configured with several cells, at least onelicensed cell (e.g., the PCell) and at least one unlicensed cell. First,common DRX operation on all aggregated and activated cells configuredfor a UE is assumed as currently agreed on in 3GPP, the common DRX beingoperated by the UE on each and every of its configured cells, the DRXoperation entailing a short and/or long DRX cycle, correspondingOn-Duration periods, etc. For one specific implementation of thisembodiment to be used in combination with the currently-standardized3GPP LTE environment, reference is made to the corresponding passages ofthe background section relating to DRX for more details on how the“normal” DRX operation works. As such, the DRX-Active instruction andcorresponding consequences can be seen as an enhancement to said normalDRX operation so as to take into account the special circumstances ofscenarios where unlicensed cells are involved.

This embodiment is based on the transmission of an appropriate DRXcommand such that the UE is continuously in DRX Active Time untilreceiving the next PDCCH for a downlink transmission to be performed viathe unlicensed cell. In particular, the DRX command (termed exemplarilyDRX-Active instruction in the following) is transmitted from the eNB tothe UE such that the UE is in DRX Active Time until the eNodeB is ableto perform the next downlink transmission on the unlicensed cell, i.e.,comprising performing successfully the LBT/CCA, transmitting thecorresponding PDCCH (on the PCell, if cross-scheduling via PCell isconfigured) and transmitting the corresponding PDSCH on the unlicensedcell. After receiving said next PDCCH for the downlink transmission tobe performed via the unlicensed cell, the UE may continue with the“normal” DRX operation and thus may continue with thecurrently-configured DRX cycle.

This embodiment has the advantage that only one DRX-Active instructionis necessary so as to keep the mobile terminal in DRX Active Time aslong as necessary (compared to the previous embodiment explained inconnection with FIG. 7). It should be noted that also after receivingthe DRX-Active instruction, the UE continues with the normal DRXoperation too; the DRX-Active instruction adds a further layer to thenormal DRX operation to deal with LAA scenarios by putting the UE in DRXActive Time in more subframes, as will become clearer in the following.

A very basic schematic sequence diagram for the UE DRX operation isillustrated in FIG. 10. As apparent therefrom, it is assumed that the UEstarts the “normal” DRX operation, and continues operating according tosame in parallel also after receiving a DRX-Active instruction (thismeans that the short/long DRX cycle is operated, DRX-related timers arestarted/restarted/expired as already defined, the UE is in DRX ActiveTime in the On-Duration periods, etc). Then, after reception of such aDRX-Active instruction, the UE shall be continuously in DRX Active Timeat least on the unlicensed cell (and assuming common DRX, basically onall aggregated cells configured for the UE) for a specific period oftime. The UE is monitoring the PDCCH. In case the UE receives a downlinkcontrol information, i.e., PDDCH, it will have to further determinewhether same relates to a downlink transmission via the unlicensed cellor not. If yes, the UE stopped operating DRX according to the DRX activeinstruction (basically always in DRX Active Time) and may continueoperating according to normal DRX, thus being in DRX Active Time or not,depending on the normal DRX short/long cycle which is running all thetime in parallel, e.g., drx-related timers arestarted/restarted/expiring as defined in current specification.Therefore, this DRX-Active instruction is basically defining a newadditional Active Time condition on top of the currently-defined DRXprocedure/Active Time conditions. Upon reception of the DRX-Activeinstruction (signaling), the UE is in DRX Active Time at least until itis stopped by the reception of a downlink control information assigningdownlink resources on the unlicensed cell.

FIG. 11 is a schematic illustration of the DRX operation for a UEconfigured with two cells, where a similar scenario is assumed as forexplaining the previous embodiments. As can be appreciated from FIG. 11,a DRX-Active instruction is transmitted in subframe 8 (before expiry ofthe DRX Inactivity Timer, restarted by the last PDCCH of the 1st databurst); the DRX-Active instruction is assumed here to also restart theDRX Inactivity Timer, e.g., when the DRX-Active instruction isimplemented as a PDCCH, see later. According to the exemplaryimplementation of FIG. 11, immediately upon receiving the DRX activeinstruction, the UE will operate DRX so as to be in DRX Active Timeirrespective of any of the other DRX Active Time conditions (e.g., afterexpiry of the DRX Inactivity Timer at subframe 10). For illustrativepurposes, any signaling and processing delay for the DRX-Activeinstruction is neglected here.

This will be done until receiving the next PDCCH for scheduling adownlink transmission on the unlicensed cell, which is assumed in thiscase to take place in subframe 22. Correspondingly, upon receiving saidnext PDCCH, the UE will continue operating according to the “normal”(i.e., as currently specified) DRX operation, which will include thatthe UE will be in DRX Active Time in the subframes 22-28 since the DRXinactivity timer is running as started by the first PDCCH in subframe 22and restarted by the PDCCHs in the subsequent subframes. Following thenormal DRX operation, the UE will not be in DRX Active Time duringsubframes 29, 30 and 31, while again being in DRX Active Time during theOn-Duration subframes 32-34, and so on.

So far it was assumed that the UE, upon reception of the DRX-Activeinstruction, as soon as possible adheres to the instruction by being inDRX Active Time. In other words, the UE, immediately upon reception andprocessing of the DRX-Active instruction, operates to be in DRX ActiveTime. Alternatively, the UE may not immediately operate to be in DRXActive Time upon reception and processing of the DRX-Active instruction,but may rather delay the execution of the DRX-Active instruction forsome time. Thus, during the delay (i.e., after receiving the DRX activeinstruction but before its execution), the UE continues to operate thenormal DRX. The delay could be, e.g., predetermined or may be separatelyinstructed to the UE (e.g., also within the DRX-Active instructionitself). For example, when assuming the implementation where the MACcontrol element carries the DRX-Active instruction (see later), the MACcontrol element may also carry in a corresponding field information(e.g., 8 bits) allowing the UE to determine the delay/offset. Forexample, the delay could be indicated directly as the number ofsubframes the UE should wait until executing the DRX-Active instructionafter its reception. Alternatively, the delay could be indicated as thenumber of subframes before the starting subframe of the next On-Durationperiod of the DRX function, which has the advantage that the subframe atwhich the UE shall execute the DRX-Active instruction is unambiguous andnot dependent on the reception (and/or successful decoding) point intime (which is the case where the delay is directly indicated as thenumber of subframes to wait).

Delaying the execution of the DRX active instruction in the UE can beparticularly advantageous in those cases where the eNodeB can predict(for example based on some collected statistics regarding the channelaccessibility of the unlicensed cell) the channel occupation and thuscan predict when the next transmission opportunity would (likely) beavailable on the unlicensed cell. Correspondingly, instead of being inDRX Active Time as of receiving the DRX-Active instruction, the delaywill achieve that the UE is not in DRX Active Time at the beginning, butonly after the delay, and thus power can be saved.

This embodiment where the DRX active instruction is delayed isexemplarily illustrated in FIG. 12. When comparing same to FIG. 11, theexecution of the DRX-active instruction is effectively delayed for 10subframes, such that the UE operates according to normal DRX untilsubframe 18. Then, upon executing the DRX-Active instruction after thedelay at subframe 19, the UE is in DRX Active Time in subframes 19-21due to said DRX-Active instruction. Upon receiving the next PDCCH insubframe 22, normal DRX operation is resumed by the UE, which entails tobe in DRX Active Time due to the DRX Inactivity Timer running.

According to one implementation of this embodiment, the DRX-Activeinstruction is a MAC control element, defined specifically for saidpurpose. For example, one of the reserved logical channel ID can be usedfor identifying such a new DRX MAC control element. As apparent from thecurrent 3GPP specification TS 36.321, current version 12.5.0, subclause6.2.1, incorporated herein by reference, Table 6.2.1-1 gives values ofthe Logical Channel ID (LCID) for the Downlink Shared channel, wherevalues 01011-11001 are reserved. In order to identify a MAC controlelement as the new DRX active instruction, one of the reserved LCIDvalues could be used, such as 11001. The table could in this exemplarycase be as follows:

Index LCID values 00000 CCCH 00001-01010 Identity of the logical channel01011-11000 Reserved 11001 DRX-Active instruction 11010 Long DRX command11011 Activation/Deactivation 11100 UE Contention Resolution Identity11101 Timing Advance Command 11110 DRX Command 11111 Padding

Of course, other reserved LCID values could be used in said respect.Correspondingly, the MAC PDU subheader of the MAC control element willinclude the specific LCID value to identify the new DRX-Activeinstruction. The MAC CE itself may have a fixed size of 0 bits.

According to an alternative implementation of this embodiment, PDCCHsignaling is used instead of MAC signaling to convey the DRX-Activeinstruction. In particular, any of the available DCI formats can be usedto transport the DRX-Active instruction. In one example, the so-called“PDCCH order” of DCI Format 1A can be used to convey this message. Inparticular, as defined in subclause 5.3.3.1.3 “Format 1A” of the 3GPPspecification TS 36.212 current version 12.4.0, incorporated herein byreference, “a PDCCH order can be carried by the PDCCH or EPDCCH” for thepurpose of initiating a random access procedure. Such a PDCCH order toinitiate RACH of DCI Format 1A is very specific:

Format 1A is used for random access procedure initiated by a PDCCH orderonly if format 1A CRC is scrambled with C-RNTI and all the remainingfields are set as follows:

-   -   Localized/Distributed VRB assignment flag—1 bit is set to ‘0’    -   Resource block assignment—bits, where all bits shall be set to 1    -   Preamble Index—6 bits    -   PRACH Mask Index—4 bits, [5]    -   All the remaining bits in format 1A for compact scheduling        assignment of one PDSCH codeword are set to zero

Correspondingly, such a PDCCH order, when carrying the identification ofthe unlicensed cell in the corresponding carrier indicator field, couldbe used to convey the DRX-Active instruction. In other words, an PDCCH(DCI Format 1A), normally instructing to initiate a RACH procedure,will, in case the CIF carries the ID of the unlicensed cell, beinterpreted by the UE as the DRX-Active instruction, and the UE willthus be in DRX Active Time until receiving the next PDCCH scheduling adownlink transmission on the unlicensed cell.

This has the advantage that the PDCCH order which is already defined inthe standard can be reused as a DRX-Active command. It should be notedthat the assumption here is that a PDCCH order will not be used forunlicensed cells, since random access on an unlicensed cell is notnecessary. Normally, the PDCCH-ordered random access is used in order tosynchronize the uplink timing of the UE. However, for the case of LAA,respectively for unlicensed cells, the synchronization might be notnecessary at all or done by other means.

Of course, there are other ways to convey the DRX-Active command as aPDCCH. In particular, some bits of any other existing DCI may beredefined for said purpose. In this case, there needs to be somepredefined codepoint(s) of at least one of the field conveyed withinthis DCI or a combination of predefined codepoints of several fieldswhich indicates that remaining bits within the DCI are interpreteddifferently, i.e., indicating the DRX-active instruction or the numberof subframes the UE shall wait before executing the DRX-activeinstruction. According to yet another implementation a new DCI could beintroduced which indicates the DRX-active instruction. This new DCIcould be of very short size; however introducing a new DCI would come atthe cost of an increased blind decoding effort required for the UE.

When assuming a particular implementation in the 3GPP environment,particularly as described in the background section, one exemplaryimplementation of the solution can foresee an additional condition forthe UE to check whether a particular subframe shall be DRX Active Timeor not. In particular, currently the 3GPP technical standard 36.321,current version 12.5.0, defines in section 5.7 several conditions whichcould be extended by the following additional condition:

When a DRX cycle is configured, the Active Time includes the time while

-   -   a PDCCH for scheduling PDSCH on an unlicensed cell has not been        received after successful reception of a DRX-Active instruction

According to one specific implementation of the embodiment, the abovediscussed condition of operating according to the DRX-Active instructionuntil the reception of the next PDCCH scheduling a downlink transmissionvia the unlicensed cell, could be implemented by use of a suitabletimer. In particular, a new timer, e.g., termed LAA-related DRX timer,could be started upon reception of the DRX-Active instruction, and willbe stopped by the reception of said PDCCH scheduling a downlinktransmission on the unlicensed cell. Correspondingly, the UE shall be inDRX Active Time as long as the LAA-related DRX timer is running. Thevalue of the timer can be chosen such that it is guaranteed that the UEis still in DRX Active Time when the next transmission on the unlicensedcell occurs. For example, the value of the LAA-related DRX timer can belarger than the short/long DRX cycle.

When assuming a particular implementation in the 3GPP environment,particularly as described in the background section, one exemplaryimplementation of the solution can foresee an additional condition forthe UE to check whether a particular subframe shall be DRX Active Timeor not. In particular, currently the 3GPP technical standard 36.321,current version 12.5.0, defines in section 5.7 several conditions whichcould be extended by the following additional condition:

-   -   When a DRX cycle is configured, the Active Time includes the        time while the LAA-related DRX timer is running

The implementation as a timer has the additional advantage that there isa maximum time period that the UE is in DRX Active Time upon receptionof the DRX active instruction. Put differently, in case no PDCCHscheduling a PDSCH on the unlicensed cell is received by the UE, thetimer makes sure that the UE is not in DRX Active Time indefinitely, butonly until the timer expires.

According to a specific implementation of the embodiment, in order toallow the eNodeB to “abort” (i.e., exit) the UE to operate according tothe DRX-Active instruction, the eNodeB may transmit a correspondinginstruction for the UE to resume the normal DRX operation and thus toexit the DRX operation according to the DRX active instruction. In otherwords, such an abort instruction shall be understood by the UE as aninstruction to enter normal DRX operation. For example, the DRX MACcontrol elements already defined in the standardization can be reused insaid respect, particularly the DRX MAC control element and the long DRXMAC control element as defined in 3GPP TS 36.321, current version12.5.0, at least subclauses 5.7 and 6.1.3.9 being incorporated herein byreference. Correspondingly, upon reception of a DRX-Active instruction,the UE is continuously in DRX Active Time until the UE either receives aPDCCH scheduling a downlink transmission on the unlicensed cell or untilit receives a corresponding DRX-Active exit instruction (such as theLong DRX MAC CE).

When the embodiment is implemented as a timer, e.g., the LAA-related DRXtimer mentioned above, this timer shall be stopped when receiving thenext PDCCH scheduling the downlink transmission on the unlicensed cell,but also when receiving a DRX-Active exit instruction (e.g., the DRX MACCE or Long DRX MAC CE) as discussed above.

One specific implementation of this embodiment also considers theoperation of the cell deactivation timer that can be configured in a UE,which is a timer that, upon expiry, triggers a corresponding cell to bedeactivated. As mentioned before, the current 3GPP specification TS36.321 v12.5.0, subclause 5.13, defines an sCellDeactivationTimer whichcan be running for an SCell, where the UE shall deactivate the SCellupon its expiry. While the PCell cannot be deactivated by such a timer,this may well be the case for any of the other (un)licensed cells withwhich the UE is configured. The cell deactivation timer can be runningin the UE for each serving cell (Scell) and may thus cause theunlicensed cell to be deactivated although it should remain activated soas to be able to receive the next downlink transmission from the eNodeB.According to this specific implementation, the function of the celldeactivation timer can be ignored in said respect(deactivation/activation of the SCells can still be controlled bycorresponding explicit activation/deactivation commands from theeNodeB). Furthermore, in case the cell via which the unlicensed cell isscheduled is not the PCell, but, e.g., another licensed Scell, thisother licensed SCell shall also not be deactivated by the celldeactivation timer, and thus the function of the cell deactivation timershall be ignored in said respect too.

So far, a common DRX operation has been assumed for this embodiment.However, the principles underlying this embodiment can be also appliedto scenarios where separate DRX operation is implemented. In particular,the DRX-Active instruction could for example be only applied by the UEto the common DRX operation on the respective unlicensed cell(s) and thecorresponding scheduling cells (i.e., those cells carrying thescheduling information for the unlicensed cells, if cross scheduling isconfigured). On the other hand, the UE would continue separately withthe normal DRX operation on other serving cells, which DRX operation isseparate from the (common) DRX operation of the unlicensed cell (andscheduling cell, in case of cross-scheduling).

In the following, an improvement to the various previous embodimentswill be presented, which can be used in combination with each of them.According to this improvement, the UE would in addition be able toautonomously control the DRX Active Time for an unlicensed cell, so asto decide whether it is indeed in DRX Active Time or not. In particular,the UE could in this case monitor the traffic on the unlicensed cell. Incase it detects a transmission from another eNB or some Wifi node on theunlicensed cell, it would know that the channel is occupied (assumingthat this would also be the case for the eNB), the UE would not need tomonitor the unlicensed cell/carrier for a control channel or datatransmission from its own serving eNB (the eNB the UE has established anRRC connection with). Put in other words, the UE does not need to be inDRX Active Time as long as the unlicensed channel is utilized by someother node, since CCA executed by its own serving eNB would not besuccessful in this case.

In one specific implementation of this improvement, the UE could in saidrespect make use of information on the length of the channel occupancytime. As already the case for Wifi transmissions, the duration of atransmission burst (the channel occupancy time) is signaled at thebeginning of the burst. Furthermore, according to some exemplaryembodiments, the duration of a transmission burst performed by aneNodeB, i.e., channel occupancy time, could also be signaled in thebeginning, e.g., in the first symbols of a transmission burst. With thisinformation, a UE would be aware for how long it would not need tomonitor for signaling (control information or data) from its own servingeNB and could hence optimize the power consumption. One assumption inthis embodiment is that the UE is capable of receiving and decodingtransmission from other nodes, i.e., other eNB or Wifi nodes, on theunlicensed cell.

Further Embodiments

According to a first aspect, a method is provided for operating aDiscontinuous Reception, DRX, function at a user equipment. The userequipment is configured with at least one licensed cell and at least oneunlicensed cell and operates the DRX function. The method comprises thefollowing steps performed by the user equipment. The UE receives, from aradio base station, a DRX-active instruction to be in DRX Active Time atleast on the unlicensed cell until receiving the next downlink controlinformation related to a downlink data transmission to be received viathe unlicensed cell. In response to the received DRX-active instruction,the UE is in DRX Active Time at least on the unlicensed cell, comprisingcontinuously monitoring a downlink control channel for downlink controlinformation. According to an advantageous variant of the first aspectwhich can be used in addition to the above, upon receiving said nextdownlink control information, the user equipment continues operating theDRX function, comprising being in DRX Active Time for an On-Duration oftime and being not in DRX Active Time, according to a long or short DRXcycle of the DRX function.

According to an advantageous variant of the first aspect which can beused in addition to the above, a scheduling cell, being the cell onwhich downlink control information related to the downlink datatransmission to be received via the unlicensed cell is received by theuser equipment, is either the unlicensed cell, another unlicensed cell,or a licensed cell.

According to an advantageous variant of the first aspect which can beused in addition to the above, the DRX function is operated in commonfor the at least one licensed cell and the at least one unlicensed cell,comprising being in DRX Active Time and being not in DRX Active Time onthe at least one licensed cell and the at least one unlicensed cell atthe same time according to the common DRX function.

According to an advantageous variant of the first aspect which can beused in addition to the above, upon reception of the DRX-activeinstruction, an unlicensed cell active timer is started. The userequipment is in DRX Active Time at least on the unlicensed cell whilethe unlicensed cell active timer is running. The unlicensed cell activetimer is stopped upon reception of said next downlink controlinformation related to the downlink data transmission to be received viathe unlicensed cell. Optionally, the unlicensed cell active timer isstopped upon reception of a DRX instruction to become non-active, forexample a DRX instruction to enter a short DRX cycle or to enter a longDRX cycle.

According to an advantageous variant of the first aspect which can beused in addition to the above, the DRX-active instruction is comprisedin a control element of a Medium Access Control, MAC, protocol.Optionally, the MAC control element comprises a predeterminedidentification value indicating the MAC control element to be theDRX-active instruction.

According to an alternative variant of the first aspect to the above,the DRX-active instruction is comprised in downlink control information,DCI, transmitted on the downlink control channel. Optionally, the DCI isof the 3GPP DCI Format 1A and comprises information such that the DCI:

-   -   is processed by a user equipment as an instruction to perform a        random access procedure on a licensed cell when comprising an        identification of this licensed cell, and    -   is processed by a user equipment as the DRX-active instruction        when comprising an identification of the unlicensed cell.

According to an advantageous variant of the first aspect which can beused in addition to the above, the user equipment follows the DRX-activeinstruction either immediately upon reception of the DRX-activeinstruction. Or, the user equipment follows the DRX-active instructionafter a particular time period upon reception of the DRX-activeinstruction. Optionally, the particular time period is determined by theuser equipment based on information comprised in the DRX-activeinstruction, which for example indicates a number of subframes beforethe starting subframe of the next On-Duration period of the DRXfunction.

According to an advantageous variant of the first aspect which can beused in addition to the above, at least a scheduling cell, on whichdownlink control information related to the downlink data transmissionto be received via the unlicensed cell is received, and the unlicensedcell is not deactivated until receiving said next downlink controlinformation. Optionally, the scheduling cell and the unlicensed cell arenot deactivated upon expiry of a cell deactivation timer configured forthe scheduling cell and the unlicensed cell or upon reception of a celldeactivation instruction from the radio base station for the schedulingcell and the unlicensed cell.

According to a second aspect, a method is provided for operating aDiscontinuous Reception, DRX, function at a user equipment. The userequipment is configured with at least one licensed cell and at least oneunlicensed cell and operates the DRX function. The user equipment is inDRX Active Time for the unlicensed cell for all subframes in which theunlicensed cell is activated such that the user equipment continuouslymonitors a downlink control channel associated with the unlicensed cellfor all subframes in which the unlicensed cell is activated.

According to an advantageous variant of the second aspect which can beused in addition to the above, at least a scheduling cell, on whichdownlink control information related to a downlink data transmission tobe received via the unlicensed cell is received, is not deactivated uponexpiry of a cell deactivation timer configured for the scheduling cell.Optionally, the scheduling cell is deactivated upon reception of a celldeactivation instruction from the radio base station and is activatedupon reception of a cell activation instruction from the radio basestation.

According to an advantageous variant of the second aspect which can beused in addition to the above, the DRX function is operated in commonfor the at least one licensed cell and the at least one unlicensed cell,comprising being in DRX Active Time and being not in DRX Active Time onthe at least one licensed cell and the at least one unlicensed cell atthe same time according to the common DRX function such that the userequipment continuously monitors downlink control channels on the atleast one licensed cell and on the at least one unlicensed cell at allsubframes in which the unlicensed cell is activated.

According to an alternative variant of the second aspect which can beused in addition to the above, the DRX function is operated by the userequipment on the unlicensed cell and also on a scheduling cell in casedownlink control information for the unlicensed cell is received via thescheduling cell, such that the user equipment monitors a downlinkcontrol channel associated with the unlicensed cell for all subframes inwhich the unlicensed cell is activated. The DRX function is separatefrom at least one further DRX function according to which the userequipment operates the at least one licensed cell, comprising being inDRX Active Time and being not in DRX Active Time on the at least onelicensed cell according to the further DRX function.

According to a third aspect, a user equipment is provided for operatinga Discontinuous Reception, DRX, function. The user equipment isconfigured with at least one licensed cell and at least one unlicensedcell and operates the DRX function. A receiver of the user equipmentreceives, from a radio base station, a DRX-active instruction to be inDRX Active Time at least on the unlicensed cell until receiving the nextdownlink control information related to a downlink data transmission tobe received via the unlicensed cell. A processor of the user equipmentcontrols the user equipment to be, in response to the receivedDRX-active instruction, in DRX Active Time at least on the unlicensedcell, comprising continuously monitoring a downlink control channel fordownlink control information.

According to an advantageous variant of the third aspect which can beused in addition to the above, upon receiving said next downlink controlinformation, the user equipment continues operating the DRX function,comprising being in DRX Active Time for an On-Duration of time and beingnot in DRX Active Time, according to a long or short DRX cycle of theDRX function.

According to an advantageous variant of the third aspect which can beused in addition to the above, upon reception of the DRX-activeinstruction, the processor starts an unlicensed cell active timer. Theuser equipment is in DRX Active Time at least on the unlicensed cellwhile the unlicensed cell active timer is running. The processor stopsthe unlicensed cell active timer upon reception of said next downlinkcontrol information related to the downlink data transmission to bereceived via the unlicensed cell. Optionally, the processor stops theunlicensed cell active timer upon reception of a DRX instruction tobecome non-active, for example a DRX instruction to enter a short DRXcycle or to enter a long DRX cycle.

According to an advantageous variant of the third aspect which can beused in addition to the above, the user equipment follows the DRX-activeinstruction either immediately upon reception of the DRX-activeinstruction. Or, the user equipment follows the DRX-active instructionafter a particular time period upon reception of the DRX-activeinstruction. Optionally, the particular time period is determined by theuser equipment based on information comprised in the DRX-activeinstruction, which for example indicates a number of subframes beforethe starting subframe of the next On-Duration period of the DRXfunction.

According to an advantageous variant of the third aspect which can beused in addition to the above, the user equipment does not deactivate atleast a scheduling cell, on which downlink control information relatedto the downlink data transmission to be received via the unlicensed cellis received, and the unlicensed cell until receiving said next downlinkcontrol information. Optionally, the user equipment does not deactivatethe scheduling cell and the unlicensed cell upon expiry of a celldeactivation timer configured for the scheduling cell and the unlicensedcell or upon reception of a cell deactivation instruction from the radiobase station for the scheduling cell and the unlicensed cell.

According to a fourth aspect, a user equipment is provided for operatinga Discontinuous Reception, DRX, function. The user equipment isconfigured with at least one licensed cell and at least one unlicensedcell and operates the DRX function. A processor of the user equipmentcontrols the user equipment to be in DRX Active Time for the unlicensedcell for all subframes in which the unlicensed cell is activated suchthat the processor of the user equipment continuously monitors adownlink control channel associated with the unlicensed cell for allsubframes in which the unlicensed cell is activated.

According to a fifth aspect, a radio base station is provided forcontrolling a Discontinuous Reception, DRX, function at a userequipment. The user equipment is configured with at least one licensedcell and at least one unlicensed cell and operates the DRX function.

A transmitter of the radio base station transmits, to the userequipment, a DRX-active instruction for the user equipment to be in DRXActive Time at least on the unlicensed cell until receiving the nextdownlink control information related to a downlink data transmission tobe received via the unlicensed cell.

Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware, software, or software incooperation with hardware. In this connection, a user terminal (mobileterminal) and an eNodeB (base station) are provided. The user terminaland base station are adapted to perform the methods described herein,including corresponding entities to participate appropriately in themethods, such as receiver, transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. The various embodiments may also be performed or embodied by acombination of these devices. In particular, each functional block usedin the description of each embodiment described above can be realized byan LSI as an integrated circuit. They may be individually formed aschips, or one chip may be formed so as to include a part or all of thefunctional blocks. They may include a data input and output coupledthereto. The LSI here may be referred to as an IC, a system LSI, a superLSI, or an ultra LSI depending on a difference in the degree ofintegration. However, the technique of implementing an integratedcircuit is not limited to the LSI and may be realized by using adedicated circuit or a general-purpose processor. In addition, an FPGA(Field Programmable Gate Array) that can be programmed after themanufacture of the LSI or a reconfigurable processor in which theconnections and the settings of circuits cells disposed inside the LSIcan be reconfigured may be used.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. An integrated circuit which, in operation,controls a process for operating a Discontinuous Reception, DRX,function at a user equipment, wherein the user equipment is configuredwith at least one licensed cell and at least one unlicensed cell andoperates the DRX function, the method being performed by the userequipment, the process comprising: receiving, from a radio base station,a DRX-active instruction to be in DRX Active Time at least on theunlicensed cell until receiving the next downlink control informationrelated to a downlink data transmission to be received via theunlicensed cell; and in response to receiving the DRX-activeinstruction, being in DRX Active Time at least on the unlicensed cell,comprising continuously monitoring a downlink control channel fordownlink control information until receiving the next downlink controlinformation related to the downlink data transmission to be received viathe unlicensed cell, wherein the DRX-active instruction is included in acontrol element of a Medium Access Control, MAC, protocol, wherein theMAC control element comprises a predetermined identification valueindicating that the MAC control element is the DRX-active instruction,wherein the DRX-active instruction is included in downlink controlinformation, DCI, transmitted on the downlink control channel, andwherein the DCI is of the 3rd Generation Partnership Project, 3GPP, DCIFormat 1A and comprises information such that the DCI: is processed bythe user equipment as an instruction to perform a random accessprocedure on a licensed cell when comprising an identification of thislicensed cell, and is processed by the user equipment as the DRX-activeinstruction when comprising an identification of the unlicensed cell. 2.The integrated circuit according to claim 1, wherein upon receiving thenext downlink control information, the user equipment continuesoperating the DRX function, comprising being in DRX Active Time for anOn-Duration of time and being not in DRX Active Time, according to along or short DRX cycle of the DRX function.
 3. The integrated circuitaccording to claim 1, wherein the DRX function is operated in common forthe at least one licensed cell and the at least one unlicensed cell,comprising being in DRX Active Time and being not in DRX Active Time onthe at least one licensed cell and the at least one unlicensed cell atthe same time according to the common DRX function.
 4. The integratedcircuit according to claim 1, wherein upon reception of the DRX-activeinstruction, an unlicensed cell active timer is started, wherein theuser equipment is in DRX Active Time at least on the unlicensed cellwhile the unlicensed cell active timer is running, and wherein theunlicensed cell active timer is stopped upon reception of the nextdownlink control information related to the downlink data transmissionto be received via the unlicensed cell, and wherein the unlicensed cellactive timer is stopped upon reception of a DRX instruction to becomenon-active, including a DRX instruction to enter a short DRX cycle or toenter a long DRX cycle.
 5. The integrated circuit according to claim 1,wherein the user equipment follows the DRX-active instruction:immediately upon reception of the DRX-active instruction, or after aparticular time period upon reception of the DRX-active instruction,wherein the particular time period is determined by the user equipmentbased on information included in the DRX-active instruction thatindicates a number of subframes before the starting subframe of the nextOn-Duration period of the DRX function.
 6. The integrated circuitaccording to claim 1, wherein at least a scheduling cell, on whichdownlink control information related to the downlink data transmissionto be received via the unlicensed cell is received, and the unlicensedcell is not deactivated until receiving the next downlink controlinformation, and wherein the scheduling cell and the unlicensed cell arenot deactivated upon expiry of a cell deactivation timer configured forthe scheduling cell and the unlicensed cell or upon reception of a celldeactivation instruction from the radio base station for the schedulingcell and the unlicensed cell.
 7. An integrated circuit which, inoperation, controls a process for operating a Discontinuous Reception,DRX, function at a user equipment, wherein the user equipment isconfigured with at least one licensed cell and at least one unlicensedcell and operates the DRX function, the process comprising: receiving aDRX-active instruction to be in DRX Active Time at least on theunlicensed cell until receiving the next downlink control informationrelated to a downlink data transmission to be received via theunlicensed cell; being in DRX Active Time at least on the unlicensedcell; and monitoring a downlink control channel, wherein the userequipment is in DRX Active Time for the unlicensed cell for a pluralityof subframes in which the unlicensed cell is activated such that theuser equipment continuously monitors the downlink control channelassociated with the unlicensed cell for all of the subframes in whichthe unlicensed cell is activated, wherein the DRX-active instruction isincluded in a control element of a Medium Access Control, MAC, protocol,wherein the MAC control element comprises a predetermined identificationvalue indicating that the MAC control element is the DRX-activeinstruction, wherein the DRX-active instruction is included in downlinkcontrol information, DCI, transmitted on the downlink control channel,and wherein the DCI is of the 3rd Generation Partnership Project, 3GPP,DCI Format 1A and comprises information such that the DCI: is processedby the user equipment as an instruction to perform a random accessprocedure on a licensed cell when comprising an identification of thislicensed cell, and is processed by the user equipment as the DRX-activeinstruction when comprising an identification of the unlicensed cell. 8.The integrated circuit according to claim 7, wherein at least ascheduling cell, on which downlink control information related to adownlink data transmission to be received via the unlicensed cell isreceived, is not deactivated upon expiry of a cell deactivation timerconfigured for the scheduling cell, and wherein the scheduling cell isdeactivated upon reception of a cell deactivation instruction from theradio base station and is activated upon reception of a cell activationinstruction from the radio base station.
 9. The integrated circuitaccording to claim 7, wherein the DRX function is operated in common forthe at least one licensed cell and the at least one unlicensed cell,comprising being in DRX Active Time and being not in DRX Active Time onthe at least one licensed cell and the at least one unlicensed cell atthe same time according to the common DRX function such that the userequipment continuously monitors downlink control channels on the atleast one licensed cell and on the at least one unlicensed cell at allof the subframes in which the unlicensed cell is activated.
 10. Theintegrated circuit according to claim 7, wherein the DRX function isoperated by the user equipment on the unlicensed cell and also on ascheduling cell in case downlink control information for the unlicensedcell is received via the scheduling cell, such that the user equipmentmonitors the downlink control channel associated with the unlicensedcell for all of the subframes in which the unlicensed cell is activated,and wherein the DRX function is separate from at least one further DRXfunction according to which the user equipment operates the at least onelicensed cell, comprising being in DRX Active Time and being not in DRXActive Time on the at least one licensed cell according to the furtherDRX function.